The proposed investigations are intended to provide new information of clinical importance on the functional consequences of restricted injuries to peripheral nerves or the spinal cord. The injuries are restricted to an individual nerve with a small peripheral distribution or to a single spinal pathway, so that non-debilitating models can reveal important principles that will aid in the diagnosis, management and treatment of more severe injuries that are seen clinically in the human population. The spinal lesion studies are conducted with non-human primates, because the organization of the spinal pathways of primates differs considerably from that of other mammals. In addition, we will utilize powerful techniques of nuclear magnetic resonance (NMR) imaging to evaluate the extent of the spinal cord injuries, which will enhance the ability to correlate functional deficits with the location and extent of a lesion. Two investigations will evaluate sensory capacities that are diminished or remain after interruption of ascending pathways on one side of the spinal cord. The first of these will provide the first thorough series of tests of proprioceptive sensations (providing information about the movement and position of the limbs) following a lesion of the ipsilateral dorsal column or lateral column. The results of this study will provide needed information concerning mechanisms of motor deficits that occur with spinal injuries. Also, the effects of dorsal column lesions on modulation of tactile sensitivity will be investigated. Previous studies have indicated that some impairments of touch sensations following interruption of the dorsal column result not from a loss of information but from activation of an inhibitory process by the lesion. Further understanding of this inhibitory process may suggest strategies to circumvent it, for the purpose of restoring tactile capabilities. Two other investigations are concerned with mechanisms responsible for generation of pain following injuries to peripheral nerves or the spinal cord. The first of these seeks to reveal whether partial injuries to peripheral nerves of rats result in an enhanced perception of pain in the region innervated by that nerve. If the mechanism for generation of this abnormal sensation can be determined, then treatments of peripheral nerve injuries for prevention of pain could be developed. Another investigation seeks to reveal the characteristics of spinal cord lesions in monkeys that can generate abnormal pain sensitivity. Current hypotheses concerning mechanisms of chronic pain from spinal lesions will be addressed by interrupting spinothalamic or lemniscal pathways. Identification of the mechanisms for pain of central origin could lead to improved treatments for control of chronic pain. The stimuli utilized in these studies are brief, non-injurious and easily tolerated by monkeys and humans. These experiments provide highly quantitative evaluations of changes in sensory capacities over time following clinically relevant restrictions of input.